The invention represents a development of an ultrasonic monitoring system for the interior of a motor vehicle and which, per se, is previously known, for example, from German reference DE-A1-2,817,492. This known system already permits the monitoring of the interior of a motor vehicle with relatively little effort.
In addition, U.S. Pat. No. 3,805,223 discloses an ultrasonic monitoring system having a single ultrasonic emission element and a single ultrasonic reception element--both elements having a more or less marked directional characteristic--which system is employed for the observation of fish or aquatic animals in a region filled with water--for example in an aquarium or in a pool. The main lobes of the directional characteristics of these elements are set to be oriented so that repeated reflections via a plurality of boundaries of the region filled with water--that is to say, for example, via the panes of the aquarium--are also clearly utilized, so that the movements of the fish through the monitoring system can be automatically registered not only on a rectilinear path in the water, but in a larger space in the water.
The invention presupposes that the ultrasonic monitoring system which is described below and which is shown in FIG. 1 also forms part of the prior art:
The motor vehicle shown in FIG. 1 exhibits, inter alia, six panes, namely four side panes VS1, VS2, HS1 and HS2, as well as lateral panes F and H at front and rear, namely a front pane F and a rear pane H.
Fitted on the internal surface of the roof of the motor vehicle, in the vicinity of the so-called B spars, i.e. between the front and rear side panes VS1/HS2, VS2/HS1, there are four radar elements SE1 to SE4 for ultrasonic radar, which radar elements, as is very frequently the case with radar systems, are employed in each instance both as emission elements with a marked directional characteristic and also as reception elements with a marked directional characteristic.
The main lobes of the emission directional characteristics and of the reception directional characteristics of all four radar elements SE1 to SE4 are, at least to a large extent, oriented in each instance in the same direction. In this case, the interior of the motor vehicle is thus, so to speak, monitored by a total of four emission elements and four reception elements, of which, however, each emission element forms a physical unit with a reception element. In this case, the four radar elements SE1 to SE4 monitor in each instance, more or less, only approximately one quarter of the motor vehicle interior surface represented in the plan view.
To this end, in operation, the four radar elements SE1 to SE4 emit ultrasonic pulses at a specified frequency or in a specified frequency pattern, in each instance towards a specified region on a lateral pane F, H, in each instance to the left or to the right of the center of the lateral pane, or into adjacent regions close to the pane; in this case, these four radar elements, after their switch-over, receive in each instance as reception elements especially that ultrasound which was reflected by the regions which were ensonified by these radar elements themselves in the emission phase. The received signals are converted into electrical signals in the reception elements, and, thereafter, are passed to one or more control circuits which, for their part, evaluate these signals.
In this case, these four radar elements SE1 to SE4 also monitor to a greater or lesser extent the side panes which are adjacent to the principal axis of the main lobe of the ultrasonic beam and which belong to the quarter of the interior surface. Within this ensonified region, including the pertinent side panes, certain reflections also occur, so that, via the main lobe of the reception directional characteristic of these four radar elements SE1 to SE4, certain components of ultrasonic waves which are also repeatedly reflected within the ensonified region are also received and jointly evaluated. These received, repeatedly reflected ultrasonic waves are then, however, in each instance emitted entirely, or at least preferably, by the same radar element (i.e. less from the other three radar elements) into this region.
Specifically, in the case of the example shown in FIG. 1, it is typical that the principal axes or main lobes of the emission directional characteristics and of the reception directional characteristics of all radar elements SE1 to SE4 coincide to a large extent in each instance. In any case, the principal axes of the emission directional characteristic and of the reception directional characteristic, considering each individual path of the radar elements SE1 to SE4, are not intentionally oriented in entirely different directions, in order in a controlled manner to receive as far as possible only such an ultrasonic flow as was originally emitted by another emission element in entirely different directions and thus into entirely different regions of the interior of the motor vehicle and which is intentionally received and evaluated only after repeated reflections, which are distributed over large regions of the interior of the motor vehicle.
In addition, German reference DE-C2 2,938,969--which is equivalent to European reference EP-B1-26,385 discloses an ultrasonic monitoring system in which, by means of the storage of echo profiles and by means of adaptive progressive adaptations of the system to such movements, automatic elimination takes place of those disturbances which are generated by movements which are intrinsically harmless, e.g. of air striations and fans and the like.